This invention relates generally to temporary cardiac assist devices used to assist the operation of a failing, traumatized or infarcted heart for a limited period until either the heart recovers or more definitive treatment can be provided. In particular, it relates to so-called intra-aortic balloon pumps. Such a pump does not require major thoracic surgery to connect it to the circulation but is a collapsible structure which may be introduced into an easily accessible artery, such as a femoral, and may then be guided into some portion of the aorta, where it can be employed to assist the left side of the heart. In the usual "counterpulsation" mode of employment, the balloon is pneumatically inflated during diastole to increase blood pressure and deflated during systole to lower the pressure load upon the ventricle. This device and its mode of operation was described in a paper by Moulopolous, Topaz and Kolff, "Diastolic Balloon pumping in the Aorta--A Mechanical Assistance to the Failing Circulation", American Heart Journal (1962) 63, p. 669.
Since intra-aortic balloon pumps can be applied with relatively minor surgery and fairly standard vascular catheterization procedures, and afford some useful assistance to the left heart, they are well regarded. However, they provide much less pumping assistance than one would desire, for at least three reasons: first, the conveniently available volume within the aorta is not large compared to the desired stroke volume of the heart, particularly because of the necessity to avoid occluding important arteries such as the carotids and renals; second, the elastic compliance of the aortic wall makes the effective displacement of the balloon less than its geometric displacment, and third, the balloon is merely a phase shift device and not by itself, a true pump. Many inventions have been addressed to the alleviation of these problems: For example, U.S. Pat. No. 3,054,662 to R. T. Jones shows how to attain better pump fluid dynamics, and U.S. Pat. No. 3,692,018 to Goetz and Goetz shows how to direct the limited available flow predominantly to the critical brain and heart circulations. Although this limits the pump's effectiveness, the balloon pump is placed within the descending aorta in order that emboli which may be produced do not pass up the carotid arteries to the brain.